Losing fuel after loading game

I've encountered something of an annoyance. Everytime I load the game, I lose all the fuel that was left in a barrel which my ship was using when the game was saved. Is this a bug, and if yes, is it something I can fix?

In case it's relevant: I have both the original game and Zubmariner (from GOG). I used GOG Galaxy to install them, and according to GOG Galaxy my version of the game is 2.2.2.3129(3130 DLC)a.